Ocean shipping accounts for approximately 3% of global greenhouse gas emissions — and as ESG reporting requirements tighten, shippers are increasingly expected to measure, report, and reduce the carbon footprint of their freight.
This guide explains how carbon emissions from ocean shipping are calculated, what the regulatory landscape looks like, and how to start tracking your shipping carbon footprint.
How ocean shipping emissions are calculated
Carbon emissions from ocean shipping are typically calculated using the distance-based method: emissions = distance × weight × emission factor. The emission factor depends on the vessel type, size, fuel type, and operational efficiency (speed, capacity utilisation).
The most commonly used framework is the Global Logistics Emissions Council (GLEC) framework, which provides standardised emission factors for different transport modes. For ocean shipping, emission factors are expressed in grams of CO2 per tonne-kilometre (g CO2/tkm), and vary significantly between vessel types. A large container vessel (15,000+ TEU) operating at high utilisation produces roughly 5-8 g CO2/tkm. A smaller feeder vessel (1,000-3,000 TEU) might produce 15-25 g CO2/tkm.
The challenge for individual shippers is getting accurate data. You need to know the actual route (including transshipments), the vessel carrying your cargo (to determine its emission factor), and ideally the actual speed and fuel consumption for that specific voyage. Carrier-reported data often uses generic averages rather than voyage-specific calculations.
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Visibility that goes beyond just where your cargo is
Why accurate measurement matters
Inaccurate carbon measurement has real consequences. Under-reporting exposes your organisation to regulatory risk as emissions reporting requirements become mandatory. Over-reporting wastes money if you're purchasing carbon offsets or credits based on inflated numbers. And generic averages — which don't account for the specific vessel, route, or carrier — make it impossible to make informed decisions about reducing your shipping footprint.
For example, two shipments on the same trade lane can have very different emissions profiles if one uses a modern, fuel-efficient vessel on a direct service and the other uses an older vessel with a transshipment connection. Without voyage-specific data, you can't distinguish between them.
The regulatory landscape
The regulatory requirements for shipping emissions reporting are tightening rapidly. The EU Emissions Trading System (EU ETS) now covers ocean shipping, requiring carriers to report and pay for emissions on voyages to, from, and within the EU. The IMO's Carbon Intensity Indicator (CII) rates vessels on their operational carbon efficiency. The Corporate Sustainability Reporting Directive (CSRD) in Europe requires large companies to report Scope 3 emissions — which includes upstream and downstream transportation. And the SEC's climate disclosure rules in the US are requiring publicly traded companies to report material climate-related financial risks.
For shippers, this means that emissions data from your freight operations will increasingly need to be reported to regulators, investors, and customers — and "we don't track it" is rapidly becoming an unacceptable answer.
How to reduce your shipping emissions
Once you can measure accurately, you can reduce strategically. Choose carriers with newer, more efficient vessels — the emission difference between a 2010-built and a 2024-built container vessel can be 30-40%. Prefer direct services over transshipment routes — each additional port call adds emissions from berthing, cargo handling, and the feeder vessel. Optimise container utilisation — a half-empty container produces the same vessel emissions as a full one but carries half the cargo. Consolidate shipments where possible. And consider the trade-off between speed and emissions — slow steaming reduces fuel consumption (and emissions) significantly but extends transit times.
How to track your shipping carbon footprint
Manual calculation using spreadsheets and generic emission factors is possible but error-prone and time-consuming. A better approach is to use a tracking platform that calculates emissions automatically based on the actual route, vessel, and voyage data for each of your shipments.
The most accurate platforms use real vessel AIS data to determine the actual route taken (not just the carrier's published schedule), identify the specific vessel and its emission characteristics, calculate voyage-specific emissions rather than generic averages, and aggregate data across your portfolio for reporting purposes.
This gives you a carbon footprint report that's both accurate and defensible — essential for regulatory compliance and ESG reporting.
CargoPilot
Visibility that goes beyond just where your cargo is
CargoPilot tracks vessel data that underpins meaningful Scope 3 reporting — route, carrier, and vessel class all in one place.